The present invention relates to a torque measuring device in a vehicle for measuring torque over a transmission arranged between a vehicle engine and a driven wheel of said vehicle.
Automatic transmissions of the Automatic Mechanical Transmission (AMT) type have become increasingly common in heavy-duty vehicles as microcomputer technology has continued to advance and has made it possible, with a control computer and a number of control elements, for example servo motors, to precision-control the engine speed the connection and disconnection of an automated clutch between engine and gearbox and clutch members of the gearbox, relative to one another, so that smooth gearshift is always obtained at the correct rev speed. The advantage with this type of automatic transmission compared to a traditional automatic transmission based on a set of planetary gears and with a hydrodynamic torque converter on the input side is first that, particularly with respect to use in heavy vehicles, it is simpler, more robust and can be produced at substantially lower cost, and second that it has higher efficiency which results in lower fuel consumption.
The automatic mechanical transmission of the type mentioned above strongly reduces the driver's gear shifting work and the driver will not need to worry about selecting the right next gear ratio when driving the vehicle. All this is taken care of within the AMT.
In order to perform gear shifts faster it is known to measure and/or estimate torque at the input shaft of the AMT so as to be able to control engine output torque in a more optimal way in order to achieve zero or almost zero torque in the AMT, when, for example, gear shift is performed without disengaging the clutch arranged between the engine and the AMT. Instead an engagement ring of the engaged gear is disengaged directly, the engine rotational speed is adapted to the new selected gear and the engagement ring of the new gear is engaged in order to engage the new gear. When the new gear is engaged the engine output torque is resumed according to, for example driver demand.
The clutch in an AMT can be of the dry plate clutch type and which is used to facilitate start-off from rest and disengage the transmission from the engine at some or all gear shifts. In general, there is a damper hub integrated in a dry plate clutch. Adequately designed, this damper hub reduces torsional vibrations from the engine and spares the transmission downstream of the clutch. In this context the term “downstream” is defined as a direction after a particular point in the direction of power transfer through the transmission. A damper hub usually has a number of helical springs arranged circumferentially on the driven disc that transfers torque from the engine flywheel to the input shaft of the transmission. Some designs are shown in DE102 20 205.
In order to be able to control disengagement and engagement of engagement rings in the gearbox, the engine torque has to be controlled so that zero or almost zero torque is prevailing over the AMT. One way to measure torque in such transmission arrangement is magnetostriction, which means that the AMT input shaft is magnetized with a predetermined magnetic pattern. Micro twisting of the input shaft as torque is applied is measured with electromagnetic coils arranged outside and in a contactless relationship relative the input shaft. The electromagnetic coils measure changes in permeability of the magnetic pattern, which changes are proportional to the torque twisting the shaft. An example of such a system is disclosed in for example U.S. Pat. No. 4,976,160.
Instead of measuring, the torque on the input shaft an alternative solution is to measure torque over the clutch. U.S. Pat. No. 4,683,746 discloses an arrangement for measuring the torque applied on the input shaft of a transmission by measuring the compression of clutch damper helical springs arranged in the clutch between the engine and the transmission. A certain compression distance of the spring corresponds to a certain torque applied over the clutch.
WO 2001/73389 discloses a sensor for non-contact detection of torque on a shaft by measuring the resonance frequency of a string attached to two collars on the shaft. As the shaft is twisted the string will increase or decrease its pretension, and thereby change its lateral vibration resonance frequency. By measuring the prevailing resonance frequency it is possible to indirectly determine the torque applied over the shaft. The string is radiated with microwave energy and a modulation of the microwave signal is caused by the mechanic oscillation of the string. The modulation is translated to a corresponding torque value by a signal processing device.
The known examples suffer from various drawbacks, such as slow response times, insufficient accuracy for use in AMT transmissions, expensive sensor components or complex and/or sensitive sensor arrangements.
It is desirable to come up with an alternative relatively cheap, robust, sufficiently accurate and fast torque measuring device in a vehicle transmission.
The invention, according to an aspect thereof, relates to a torque measuring system a vehicle transmission comprising a clutch assembly having at least a two part, rotatable torque transmitting member. A first part can be a part of or be connected to a flywheel driven by a prime mover, such as an engine. A second part can be a part of or be connected to an input shaft for a transmission, such as a gearbox. The transmission can be an automatic mechanical transmission. The two parts of said torque transmitting member are angularly movable relative to one another against the compression of at least one damper spring pack. An actuator with a non rotatable cylinder is provided for controlling the clutch. Although the torque measuring system according to the invention is primarily intended for friction clutch assemblies, the invention can also be applied to hydrodynamic clutches and torque converters.
A device for radiating and receiving wave energy is arranged to irradiate said damper spring pack in order to receive a reflected modulation signal proportional to the current resonance frequency of said damper spring pack, and where said modulation signal representing a measured mechanical resonance frequency is arranged to be converted to a torque value by a signal or data processing device, which torque value corresponds to the actual torque over said clutch. Torque values are determined continuously while the part comprising spring packs is rotated, in order to monitor the torque over the clutch. The resulting torque values can be used in a target gear selection function, for instance for determining when a gear change can be carried out.
The torque measuring system according to the invention is characterized in that a device for exciting, or radiating, and receiving wave energy is arranged to radiate a damper spring pack of a clutch. Suitable devices for this purpose are devices for emitting electromagnetic radiation, such as pulsed electromagnetic radio waves, microwaves, millimetric or sub-millimetric radio waves. Alternatively, devices for emitting acoustic signals can be used, for instance, for emitting ultrasonic signals. The device can comprise separate transmitter and receiver units arranged spaced apart or an integrated transmitter and receiver unit. In the subsequent text these alternatives will be referred to by the collective term “device”.
Said wave energy is reflected back from the damper spring pack in order for the device to receive a modulation signal, for instance an amplitude modulation signal, created by a current mechanical resonance frequency of said damper spring pack. Said measured mechanical resonance frequency is translated by a signal processing device to a torque value, which corresponds to the actual torque prevailing over said clutch.
The device for radiating and receiving wave energy is arranged in a suitable location from which a transmitted signal can reach the at least one spring pack and be reflected back to said device. According to a first example, the device for radiating and receiving wave energy is arranged between said spring packs and a radial diaphragm spring connecting the actuator and the clutch. According to a second example, the a radial diaphragm spring connecting the actuator and the clutch is arranged between said spring packs and said device for radiating and receiving wave energy.
Due to tolerances in the production of these spring packs and tolerances in the spring pack mounting, variations in the compression and/or resonance frequency for a certain torque over the clutch can occur between said different spring packs for a certain torque.
According to one example the signal processing device can be programmed to calibrate the measurements for one of the spring packs in the clutch. The device for radiating and receiving wave energy is then arranged to radiate wave energy to a single spring pack, whereby a torque value is determined for said spring pack. Said spring pack can for example be identified as the one with the lowest or highest mechanical resonance frequency.
In a further example and in order to be able to program the signal processing device so that it can identify the right, damper spring pack, a first distance between two of the six spring packs can differ somewhat compared to the other distances between the spring packs, which other distances can be equal. In this way, when the clutch is rotating, the time passing by between when a first spring pack has passed and to when the next spring pack passes can be identified. Thus, the right spring pack can be the one which follows after said first distance, which differs from the other distances. Said first distance can be longer or shorter compared to the other distances.
In a further example and in order to be able to program the signal processing device so that it can identify the right damper spring pack, a marker can be arranged adjacent the right damper spring pack. This marker can be a projection or a recess/aperture in the outer plate which affects the modulation of the electromagnetic radiation in such a way as to be identifiable. In this way, when the clutch is rotating, the right spring pack can be identified as the one that follows the marker in the direction of rotation.
Alternatively, the device for radiating and receiving wave energy is arranged to radiate wave energy to at least two spring packs, whereby the signal processing device is arranged to determine an average torque value for said spring packs. Ultimately, this can involve radiating and receiving individual modulation signals to and from each spring pack, respectively.
The reflected modulation signal received by the device is preferably an amplitude modulation signal. As stated above, the device is arranged to radiate wave energy in the form of electromagnetic, radiation or acoustic wave energy towards at least one spring pack.
In order to maintain accurate torque value readings, the signal processing device can be arranged to perform a recalibration when a first vehicle condition corresponding to a first torque level and a second vehicle condition corresponding to a second torque level have been detected. Said first vehicle condition can for example be a condition where zero torque is prevailing and said second vehicle condition where a maximum torque is prevailing. The relationship between the change in resonance frequency corresponding to zero torque and up to the resonance frequency corresponding to the maximum torque is linear so the resonance frequencies corresponding to different torque levels between said two different known torque levels, such as zero torque and maximum torque, can be calculated. The recalibration is necessary since the size of the windows and or the elastic properties of the spring packs can change over time. Such changes can be due to normal wear and the resonance frequency of the spring pack may therefore change accordingly over time.
The invention further involves a torque measuring method for a vehicle transmission comprising a clutch assembly having a two part, rotatable torque transmitting member, the two parts of said member being angularly movable relative to one another against the compression of at least one damper spring pack, and an actuator with a non rotatable cylinder for controlling the clutch
The method involves the steps of:                radiating wave energy towards at least one spring pack by means of a device for radiating and receiving, wave energy;        receiving wave energy in the form of a modulation signal reflected from said at least one spring pack by means of said device which modulation signal is proportional to the current resonance frequency of said damper spring pack;        transmitting the modulation signal to a signal processing device; and        converting the modulation signal to a torque value using said signal processing device, which torque value corresponds to the actual torque over said clutch.        
According to a first example, the method involves radiating wave energy to a single spring pack and determining a torque value based on the modulation signal from said single spring pack. According to a second example, the method involves radiating wave energy to at least two spring packs and determining an average torque value based on the modulation signals from each spring pack. As stated above, torque values are determined continuously while the part comprising spring packs is rotated, in order to monitor the torque over the clutch. The resulting torque values can be used in a target gear selection function, for instance for determining when a gear change can be carried out.
The torque measuring method preferably involves receiving an amplitude modulation signal reflected from said at least one spring pack.
The method can involve radiating wave energy in the form of electromagnetic radiation or acoustic wave energy towards at least one spring pack.
According to the torque measuring method, a recalibration can be performed when two different vehicle conditions have been detected, where a first vehicle condition has a first torque level and a second vehicle condition has a second torque level which torque levels differ by a predetermined amount, as discussed above.
The invention also involves a computer program comprising program code means for performing all the steps of the torque measuring method described above, when said program is run on a computer.
The invention further involves a computer program product comprising program code means stored on a computer readable medium for performing all steps of the torque measuring method described above, when said program product is run on a computer.
The invention further involves a computer system for implementing the torque measuring method described above, said computer system comprising a suitable storage medium for storing a program for controlling a target gear selection function for the vehicle, and for receiving and storing modulation signals proportional to the current resonance frequency of at least one damper spring pack, wherein a signal processing device operable to run said program for converting said modulation signals to torque values and to control the target gear selection based on said torque values.
The advantage with the device according to the invention is that the response times and the accuracy for torque measurement is improved, which in turn allows for faster and more accurate gear changes in an AMT transmissions. The use of expensive sensor components or complex and/or sensitive sensor arrangements can be avoided, as the invention merely requires a single device for radiating and receiving wave energy arranged within sensor range from a spring pack. As the device is not required to be located in the immediate vicinity of a shaft, as in the case of a Hall sensor or a magnetorestrictive sensor, less space is required for the system according to the invention.